This application is based on application Ser. Nos. 10-1999-0020656 and 10-2000-0007342 filed in the Korean Industrial Property Office on Jun. 4, 1999 and Feb. 16, 2000 respectively, the contents of which are incorporated hereinto by reference.
(a) Field of the Invention
The present invention relates to a process for preparing polyolefin polymerization catalysts, more particularly to a process for preparing polyolefin polymerization catalysts in which activities are superior during polyolefin polymerization, average particle sizes of polymers to be prepared are large, polymers of undesirable fine particles (particles having diameters of less than 100 xcexcm) are notably less in amount, and polymers showing a wide range of Melt Flow Ratios from 21.6 kg to 2.16 kg can be prepared.
(b) Description of the Related Art
Sizes of polymers polymerized using Ziegler catalysts are influenced by sizes of generally used catalysts. Technologies controlling sizes and particle distributions of Ziegler catalysts during catalyst preparation are important keys for producing polymers having desirable particle sizes because of this replication phenomena.
During polyolefin polymerization using existing inhomogeneous Ziegler-Natta catalysts which are generally prepared by contacting titanium chloride after pretreating magnesium chloride with ethanol and adding organic aluminum, a method for improving particle shapes of Ziegler polymerization catalysts is to replace catalyst supports, wherein silica and alumina are supports which have frequently been used.
However, these supports have some demerits as follows. First, catalyst preparation expenses are increased when it is necessary to remove catalytic poisons such as moisture which is adsorbed by these supports, by calcinating them at a high temperature. Second, polymer particle sizes can be reduced since supports having large pores are easily broken so fine particles of undesirable catalysts can be produced due to breakage occurring when they are used as catalyst supports. Furthermore, these oxide supports have the demerit of reducing catalyst activities since they have characteristics in which catalytic poisons such as moisture and oxygen are adsorbed very fast.
Furthermore, polymers prepared when polyolefin is polymerized using existing catalysts have many fine particles, and these polymers having many fine particles cause the following problems in operating the polyolefin polymerization processes: the possibility is quite high that small holes made for fluidizing drying equipment can be clogged by the fine particles when polymers obtained from a slurry process are dried by a fluidization bed-type dryer; the transferring capacity is deteriorated when nitrogen gas is blown to transfer the dried polymer particles to a hopper, etc.; and the capability that polymers can be infused to an extruder is reduced in that the extrusion discharge volumes per unit hour are less than when the polymer particle sizes are large.
For these reasons, many technologies controlling catalyst sizes have been published, these technologies frequently consist of various processes for treating supports, and a technology among them in which supports are dissolved into a soluble solvent and recrystallized is disclosed in many literature documents.
When reviewing these technologies, it is found that the simple type of Ziegler catalyst has very low activities and has difficulties controlling polymer shapes even though it is formed by contacting magnesium chloride and titanium chloride. Although there is a process for preparing catalysts by contacting titanium chloride after pretreating magnesium chloride with ethanol and adding organic aluminum compounds such as diethylaluminum chloride, etc. to the mixture in order to complement these demerits, this process has problems in that particle distributions of the produced polymers are not uniform, and undesirable fine particles of less than 100 xcexcm are present in large quantities when the prepared catalyst activities are high.
Practically, soluble solvents such as alcohol, aldehyde, amine, etc. are frequently used since one of the most frequently used supports, magnesium chloride, has high solubilities on these solvents. When alcohols having 6 or more carbon atoms, particularly octanols among them, are used along with hydrocarbons such as decane, kerosene, hexane, etc., magnesium is completely dissolved at a high temperature of over 100xc2x0 C. so that magnesium compounds exist in the state of a homogeneous solution which is not reprecipitated even at room temperature. Solid content catalysts can be prepared from these types of homogeneous solution through various treatment processes. Solid state titanium compounds can be obtained most easily by contacting this homogeneous solution with quadrivalence titanium halide compounds such as titanium tetrachloride. This method has merits in that catalysts are easily prepared, activities are superior, polymer specific gravities are very high, and particle distributions are very uniform since solid type catalysts can be formed by lowering a solution temperature or adding nonsolvents so that the recrystallization process can be omitted, and by directly reacting homogeneous solutions of liquid phased magnesium compounds with titanium halide compounds.
Catalysts prepared by the above process are prepared by slowly adding a magnesium homogeneous solution to a titanium tetrachloride compound at a low temperature, for example xe2x88x9220xc2x0 C. Polymers in which average particle sizes are large and therefore the amount of undesirable fine particles is less, in which catalyst activities are superior, specific gravities are very high, and Melt Flow Ratio values are high, can be prepared. However, average particle sizes of polymers are notably decreased, contents of undesirable fine particles are greatly increased, and specific gravities of polymers are greatly decreased when a magnesium homogeneous solution is added to a titanium tetrachloride compound at a relatively high temperature, like room temperature, when preparing catalysts. Catalysts in which average particle sizes are large, the amount of undesirable fine particles is less, polymer activities and specific gravities are high as in catalysts prepared by adding a magnesium homogeneous solution to a titanium tetrachloride compound at a low temperature can be prepared even at a relatively high temperature, like room temperature, when titanium tetrachloride is slowly added to a magnesium homogeneous solution by changing an order of or adding reactants, thus preparing catalysts in the above preparation process. However, Melt Flow Ratio values of polymers are greatly decreased.
Therefore, catalysts prepared at room temperature can prepare polymers having various particle distributions due to very uniform polymer particle distribution and easy controlling of catalyst particle sizes during catalyst preparation, as well as polymers having a lesser amount of undesirable fine particles. The preparation process of titanium catalysts for polymerizing polyolefin in which polymers having high catalyst activities, specific gravities, and Melt Flow Ratio values (21.4 kg/2.14 kg) is needed in the polyolefin polymerization to which these catalysts are applied.
It is an object of the present invention to provide a process for preparing polyolefin polymerization catalysts in which polymers having superior olefin polymerization activities, large average particle sizes, notably lesser amounts of undesirable fine particles, and a wide range of Melt Flow Ratio values can be prepared in order to solve the above problems.
Furthermore, it is another object of the present invention to provide a process for preparing titanium catalysts for polyolefin polymerization in which catalyst particles, prepared by contacting a homogeneous solution of magnesium compounds with a quadrivalence titanium halide compound even at a relatively high temperature of over room temperature (25xc2x0 C.), can prepare polymers having various particle distributions due to the uniform polymer particle distribution and easy controlling of catalyst particle sizes during the catalyst preparation, polymers having a lesser amount of undesirable fine particles, as well as polymers having very high catalyst activities, specific gravities, and Melt Flow Ratio values, taking into account the above conventional technology problems.